Wood surfaced floor or wall coverings



April 12, 1960 C. A. A. RAYNER WOOD SURFACED FLOOR OR WALL COVERINGS Filed Nov. 9, 1954 INVENTOR MW Wm, 4 w wag/ da. m LAW 1. ATTORNEYS States WOOD SURFACED FLOOR R WALL CDVERIWGS Claude Albert Abbs Rayner, Duxford, England, assignor to Ciba Aktiengesellschaft, Basel, Switzerland, a corporation of Switzerland Application November 9, 1954, Serial No. 467,833 Claims priority, application Great Britain July 14, 1949 6 Claims. (Cl. 154-453) work, concrete, and other mineral building material. In

modern buildings in particular the main floor construction is usually of reinforced concrete or other fire-resisting mineral material, and if an ordinary wood board floor is fixed on to the concrete, shrinkage occurs and floor boards creak when walked on. If parquet blocks are used the wood blocks often become detached fromv the concrete and wobble when walked on. Moreover, in basements both fioors and walls are often damp so that wood floors will warp and are subject to dry rot. Furthermore, no wood floor will stand washing for any length of time without warping and general deterioration.

The difiiculties of fixing wood floors and like wood surface materials to mineral building materials is mainly due to the fact that those adhesives which adhere firmly to Wood do not adhere so firmly and sometimes not at all to concrete and other building materials.

In spite of the above difliculties in construction and the need for stability against washing, the dry warmth of central heating and other, deteriorating influences, wood is still the most popular material for fioorings and is used in considerable quantity for panelling.

It is, therefore, a primary object of the present invention to produce a composite article, the under part of which will have the character of stone and can be fixed to sub-floors of concrete or any mineral building material with any of the usual cements or mortars used in the building trade while the upper part is of wood and is so firmly attached to the under part that it is irns possible to break the wood away without splitting the wood and is stable against the above mentioned deteriorating influences.

A further object of the invention is to produce a composite article for flooring or panelling having a wood surface but in which the proportion of wood to the total thickness of the article is reduced to a minimum.

The present invention provides a composite article which can be fixed on to concrete, brick, stone, or any mineral building material and once fixed will remain stable against all the above mentioned influences and yet 'have the characteristics of solid wood although the thickness of wood may be only of the order 2 to 4 mm. in thickness. This is accomplished according to the invention by the particular selection of materials forming the body portion of the tile together with the method atent firmly to mineral sub-floors with the ordinary cements' Patented Apr. 12, 1960 foundation layer.

It has now been found that if a granular rocky material such as silica sand which is practically non-absorbentis selected as the foundation layer, it can be bonded together to a stone-like material with a synthetic resin binder using proportions of synthetic resin as small as 2% of the dry weight of the material and that a thin wood veneer or board can be attached so firmly to such a structure that the wood cannot be separated from the body portion of the tile (hereinafter referred to as the foundation layer) without splitting the wood.

Obviously greater proportions than 2% of binder can be used but in order to produce the composite article economically and preserve the stone-like qualities of the foundation layer, the proportion of binder in the foundation layer must be less than 10% by weight of the dry weight of the materials. Similarly, the wood ply or board (hereinafter referred to as the veneer) may be of greater thickness than 24 mm. but in order to fulfill the above objectives and attain sufficient rigidity, the foundation layer should be at least three times the thickness of the wood veneer.

The bonding of mineral materials in granular form with synthetic resin adhesives has been known for many years, for instance, for the bonding abrasive granules in the production of grinding and cutting discs, and it has been known to attach such discs to a rigid backing, but in order to stand the disintegrating action in use of these materials, the granules are required to be bonded with a high proportion of synthetic resin. Thus, an abrasive wheel has been proposed consisting of a mix of abrasive granules and hardenable synthetic resin in which the proportion of bonding agent, say, 10%, and the mix was moulded on to a rigid reinforcing backing. A surfacing layer for non-slip floorings such as stair treads has also been proposed consisting of a mixture of abrasive and fibrous material bonded with a synthetic resin in which 12-20% of the resin was said to be advantageously used and proportions up to 50% were also mentioned and the general teaching of this prior art, which is not in any way analogous to the production of wood floors, is that proportions of binder of at least 10% would be necessary to give adequate bonding.

It has also been proposed to apply a urea-formaldehyde glue to the surface of ligno-cellulosic material such as a wood board and then apply rock wool to the said glue on the said surface and to press the coated board between two hot plates. in this case the foundation layer is of wood and the synthetic resin bonding material is only a thin layer on the surface of the wood for the purpose of rendering the latter fireproof. Moreover, in order to make a solid foundation of a fibrous material such as rock wool, by pressing the latter into a layer of synthetic resin, the proportion of synthetic resin to rock wool would necessarily be considerably more than 10% which would be economically impossible in a flooring; moreover, it is important that the foundation layer should have the character of stone which is achieved with proportions of binder less than 10%.

The composite article produced according to the invention in which the body portion consists of granular nonabsorbent material such as silica sand bonded with sy thetic resin, may contain as little as 2-5 of the bonding agent because it may be applied to the granules in the form of a solution in volatile solvent or in the solid form with the aid of a solvent as diluent so that the particles, owing to their non-porous character, are coated only with the thinnest film of resin solution enabling the particles to adhere together when pressed under high pressure, giving a stone-like material which adheres very used in the building trade. The foundation layer is porous or permeable but the layer of synthetic adhesive which secures the wood surface to the foundation layer forms an impervious layer preventing contact of any moisture with the under side of the wood surface.

. In its broadest aspect, therefore, the present invention consists in a composite article or tile for use in defining the floor or wall of a building structure, said article comprising an outer veneer of wood, an inner foundation layer of at least three times the thickness of the wood veneer, said foundation being comprised of rocky granules which are substantially non-absorbent, preferably silica sand, the said granules being bonded together with a water-resistant synthetic resin in an amount less than by Weight, and preferably not more than 2-5% of the material of the foundation layer expressed in terms of the dry weight of the granules and synthetic resin, and at the inter-face of said foundation layer and outer veneer a bonding layer consisting of a high percentage of synthetic resin adherent to the wood and to the synthetic resin used in the foundation'layer.

The thickness of the veneer may be varied within the above limits according to the intended application of the composite article, for example, 2 to 4 mm. for floor tiles, 0.5 'to 1 mm. for Wall panels and for other objects a thickness determined by the amount of wear to which they are likely to be subjected.

Any bonding agent which is waterresistant and stable under the conditions of use may be used in the production of the composite articles according to the invention. Examples of such bonding agents are protein-containing materials such as glue or casein which have been hardened by formaldehyde or bi-chromate, drying oil adhesives, natural or synthetic resins.

The invention is, however, particularly concerned with the production of a synthetic resin bonded material.

The bonding agent for the granular siliceous material may conveniently be the same as that employed for bonding the wood to the body of the tile.

The siliceous material employed for making the adhesive-bonded slab should be granular and the individual particles should be substantially non-absorbent so that a minimum of binder is required to produce a strong bond and among appropriate materials sandbeing the most easily obtainable is most suitable for carrying out the invention; but materials such as broken granite or other broken rock in a granular form may be used.

. Floor tiles having a wood surface in accordance with the invention are inexpensive to produce and can be made and laid more cheaply than parquet flooring. They are attractive in appearance, and according to the properties of the adhesive used in their manufacture, they may be made resistant to damp or completely resistant to water to the extent that no disintegration takes place after immersion in water for several days, and, after drying out at normal air temperatures suffer no ill-effect. Similarly, slabs of panelling may be afiixed firmly and easily to rough and damp walls and form a completely damp-resistant wall panelling. These floor tiles or wall panels may be fixed, for example, on a concrete floor or rough brick wall by the use of cement or lime mortar in the usual conventional practice with concrete tiles, alternatively a bonding material such as bitumen may be used.

A method of producing the floor tile or wall panelling unit or other object, comprises filling into a flat mould a mix consisting of the siliceous granular material (for example, sand) and a synthetic resin binder, and placing on top or underneath the granular mix a wood veneer or plywood sheet or wood board, coated on the side in contact with the granular mix with an adhesive and pressing the whole together at a sufficient temperature and pressure to cause the binder to harden into an integral slab, the wood surface of which will form the floor or panel or other surface.

It is desirable in some cases to bond a wood veneer or plywood board to both surfaces, for example, in order to give greater strength under bending loads when floor tiles are used to span the distances between joints.

By suitable selection of theadhesive binder, for example, a synthetic resin and a hardening catalyst as hereinafter more particularly described, the bonding may be effected by pressure at atmospheric temperature. Whether heat is employed or not in the pressing operation before applying a static pressure, it may be desirable to subject the mix to vibration or ramming in order to consolidate the mass.

In order to make water-resistant composite articles any of the well-known water-resistant synthetic-resin bonding materials may be employed such, for example, as ureaformaldehyde, melamine formaldehyde or mixtures thereof, phenol formaldehyde including cresol and resorcinol-formaldehyde resins, and epoxy resins; the epoxy resins impart particularly good water-resistance to the foundation layer and excellent adhesion between the foundation layer and the veneer. Similarly, materials which are potentially resinous, such as methylol compounds of urea ormelamine in which resin formation takes place during reaction at elevated temperatures, may be used. It has been found that although phenol formaldehyde resins have an absolute water resistance, when such resin is used in making the article, the article is subject to drop in strength over a period of time, say six months if it is exposed to alternating high and low humidity or complete immersion in water. Actually epoxy resins which are not absolutely water resistant give better results because, when such resins are used in making the article no appreciable drop in strength has been experienced over a period of time, and yet the article is rendered absolutely water resistant, even under excessive exposure to moisture.

Where heating is required for the curing of the resin binder, high frequency di-electric heating may be used as the source of heat, provided suflicient power loss takes place in the sand mix either by reason of the characteristics of the resin binder or by the addition of some substance which will give the resin binder a sulficiently high loss factor without interfering with the adhesive qualities, e.g. a small proportion (0.05 to 0.1%) of carbon black or aluminium powder.

In order to facilitate the escape of water vapour andother gases when curing the veneered tile, in particular when effecting this by-the application of heat, it is desirable to use a mould made from a porous material, such, for example, as the inorganic material used for the manufacture of filter tiles as used in the chemical industry, but metal moulds may be preferred because they are more durable, in which case small holes may be drilled therein as convenient. Similarly, when high frequency di-electric heating is employed and an electrode is placed in direct contact with the mix, this electrode may with advantage be made of a sintered porous metal. In the manufacture of floor or Wall tiles or other similar objects, it is desirable to fill the moulds with the sand mix by striking off the'top surface. This requires the sand or similar material when mixed with an adhesive to have negligible green strengt Also, during pressing the amount of consolidation which results from the pre-determined travel of, for example, a ram, is dependent on the green strength. If the green strength is high, the amount of consolidation may be insufficient to produce a satisfactory moulding. On the other hand, if the mix is free-flowing by reason of. the absence of green strength, maximum consolidation may be reached before the ram has travelled its full distance. Hence, it Will be appreciated that the ability to make tiles or other objects of a pre-decided thickness by this method depends very much on the green strength of the mix. 7

As already stated, absence of any appreciable green strength resulting in a free-flowing material may be obtained by one of two methodsi (1) by mixing the sand or other similar material with an adhesive in solution and allowing all the solvent to evaporate; (2) by introducing sufiicient solvent via the adhesive or adding it during mixing, such that a relatively free-flowing wet mix is produced.

The former method has been found to result in the foundation layer having rather inferior strength unless increased amounts of adhesive are used.

The latter method is more satisfactory but may have the effect of diluting the adhesive applied to the wood and reducing the strength of the bond. This is particularly noticeable in the use of phenol-formaldehyde resins in solution in Water or organic solvents.

It will be seen, therefore, that a wet mix is desirable for making satisfactory sand resin mouldings but a dry mix is desirable if the maximum amount of adhesion is required between the wood veneer and the sand mouldmg.

This dificulty may be overcome by the use of mutually precipitating resin solutions as will be shown hereinafter.

In carrying out the manufacture of the composite articles, single moulds may be used to make each article separately and these may either be cured by means of a press capable of applying sufficient pressure to ensure good contact between the foundation layer and the wood veneer and capable of providing sufficient heat should the adhesive require an elevated temperature to effect cure. Alternatively, the composite article may be pressed sufficiently to consolidate the mass, and contact maintained between the foundation layer and the veneer by means of a static weight or a clamp.

Another method which is particularly applicable to the manufacture of flat objects such as floor or wall tiles, consists of coating a large sheet of veneer with a suitable adhesive and laying thereon an open grid whose mesh conforms to the dimensions of the article to be made, e.g. floor tile. The meshes are then filled with a mix of sand and binding adhesive, and a pressure plate which gives the imprint of a wafile pattern is laid on the top of each. The whole assembly being then cured in a press with or without heat according to the requirements of the adhesives or binding agents. On removal the grid is withdrawn and the wood trimmed to the size and shape of the article which is determined by the inside measurements of the mesh.

A further method is to make large area composite articles and to cut these into the required shapes and sizes by means of an abrasive disc cutter.

, If suflicient adhesive binder is incorporated in the sand or other suitable material, it is unnecessary to coat the wood with an adhesive; but it is more economical to use a small amount of adhesive as a binding material and apply a coating of adhesive to the wood.

Provided the articles made according to this invention incorporate adhesive binding agents which are capable of withstanding the temperatures involved, and they are affixed to a concrete base by means of a heat-resistant material, for example, sand and cement, the floor may be heated from underneath without any adverse effect on the tiles. Sub-floor heating has been found to be satisfactory with a veneer temperature of 50 C. maintained for six months. In order to impart a high degree of stiffness in relation to the weight, articles made according to this invention, particularly floor tiles, may be made with a waffle pattern in the adhesive-bonded sand moulding.

A particularly suitable sand is that known as Leighton Buzzard sand and having a particle size such that about 75% passes through a 30 mesh sieve and is retained by a 52 mesh (British Standard Specification 410-1931). Sand having a larger particle size may be used, thus 6 effecting some economy in the amount of adhesive re quired to produce satisfactory bonding of the particles.

As would be expected, I have found that the mechanical strength of the foundation layer, especially after prolonged immersion in water, is improved if a sand having a wide range of particle size is used. However, sand cannot be obtained which is as fine as many available substances and so in order to effect further improvement I incorporate additionally a finely-divided substance which is inert to the adhesive; I have found that provided an acid adhesive is not used, the incorporation of a small percentage of precipitated calcium carbonate is advantageous.

Those grades of sand classed as foundry sands are preferred to those classed as building sands.

Screened granite having a particle size of between 8 and 18 mesh (British Standard Specification 410-1931) has been used successfully.

It has been found that certain rock-like materials, for example, granulated Ketton stone, owing to their absorbent nature, require an uneconomically large amount of adhesive binder to produce a satisfactory article such as a floor or wall tile.

Floor tiles have been made using pressures from 1 to 1000 pounds per square inch. I prefer an initial consolidating pressure of to 500 pounds per square inch, but do not wish to confine myself to these limits. Much depends on the green strengths of the mix and there is no point in applying a higher pressure than that needed to consolidate the mix. A low green strength requires only light pressure. A point is soon reached where pressures of considerable magnitude produce only aninappreciable consolidation.

After the initial pressure required to consolidate the sand or similar mix, a relatively light pressure only is required to maintain the wood veneer flat or retain it in whatever other shape is desired.

In making floor tiles, a sheet of rubber may be interposed between the wood surface layer and the granular foundation layer if the rubber is first treated to cyclise the surfaces, e.g. by immersion in concentrated sulphuric acid, as will be shown more in detail hereinafter. This gives a resilient tread to the tile.

Within the economical limits of adhesive used to bind the sand or similar particles together, the moulded articles described are porous and absorbent up to the area where the resin content in the moulding is high due to migration by capillarity or otherwise of the adhesive which has been applied to the wood; at this point, the higher concentration of resin in the sand provides a complete moisture barrier. As a result, floor tiles laid on damp floors do not permit rise of moisture through the tiles.

The accompanying drawing illustrates a tile made in accordance with the invention, wherein:

Figure 1 shows a tile in perspective from above, a part being broken away to disclose the underneath contour, and

Figure 2 shows a section through the tile.

In the drawing, 1 is the surfacing layer of wood, 2 is the foundation layer, and 3 (Figure 1) shows the waffie surface underneath (shown in broken lines in Figure 2).

The following examples illustrate the nature of the invention and the manner in which it may be carried into effect, the parts and percentages given being by weight:

Example I A wood veneer is coated on one side with melamineformaldehyde resin adhesive. This veneer is then laid on the bottom surface of a mould with the adhesive layer uppermost. A mix consisting of parts of dry sand, 16 to 30 mesh (British Standard Specification 410-193 1) (Le. a mesh aperture of 1.003 mm.), 2 parts of solid melamine-formaldehyde resin adhesive, and 2-4 parts of water, .is'placed in the mould; a catalyst such as amm nium chloride may be used to accelerate curing. A pressure of from /2 to 10 pounds per square inch is then applied and the whole cured by heating in a hot press or oven at a temperature of 95 C. or electrically by means of a high frequency generator or by infra-red heating.

Less than 2% resin may be added but the strength of the sand tile is reduced. For example, with 2% resin the tensile strength is 350-400 pounds per square inch, and with 1%, 200-250 pounds per square inch. Compression strength is about 2,000 per square inch and 1,700 per square inch respectively.

Example 11 hol, and 0.05 part of carbon black is then placed in the mould, and this is then subjected to mild vibration. A pressure of /2 to 10 pounds per square inch is applied and the whole cured by means of high frequency dielectric heating.

Example 111 An aqueous solution of a melamine-formaldehyde resin having a limited solubility in water is used to coat the wood at a spread of 3 pounds per 100 square feet. A so-called spirit-soluble phenol-formaldehyde resin is used in the sand mix in the ratio of 100 parts of sand to 3 parts of a 70% solution in methylated spirit. The latter resin may be slightly water tolerant but should be of such a nature that it is precipitated on addition of a considerable amount of water. Similarly, the aqueous solution of melamine-formaldehyde resin may tolerate the addition of a small amountof organic solvent, for example, ethyl alcohol or acetone.

The resins themselves are compatible after their respective solvents have evaporated. It is, therefore, important to select resins in which no incipient curing takes place before the evaporation of a substantial amount or all of the solvent has taken place.

By this method, the use of a wet and free-flowing sand-resin mix results in both a well-bonded moulding and excellent adhesion to the wood veneer.

Example IV A wood veneer is coated on one side with an oilsoluble phenolic resin. This veneer is then laid on the bottom surface of a mould with the adhesive layer upper- Example V 100 parts of Leighton Buzzard sand are mixed with 5 parts of an aqueous urea-formaldehyde resin adhesive having a resin content of 70%, the mixture placed in a metal mould and a wood veneer, coated with a similar resin, which may with advantage incorporate coarse sawdust, as previously described, is placed on the top. The whole is heated under pressure and preferably some heat is used to accelerate cure. Melamine formaldehyde resin, for example, 10 to 20%, based upon the weight of the urea resin, may be incorporated with the latter to impart higher water resistance. Similarly, melamine or resorcinol, for example, 10 to 20%, on the weight of the urea resin, may be added.

8 Example VI A wood veneer is coated with the phenol-formaldehyde resin adhesive used in Example II and dried. This is then placed on the bottom of a metal mould on which is placed a mix comprising broken granite of a particle size between 8 and 52 mesh (British Standard Specification 410-1931) and mixed with 2% of its weight of an alcoholic phenolic resin solution (75% resin content). A pressure is applied to the surface of the granite and the whole cured at elevated temperature while maintaining a pressure of, for example, 1 to 10 pounds per square inch.

Example VI] A wood veneer is coated on one side with the phenolforrnaldehyde' resin adhesive used in Example II and dried. The grid is then placed in position on the coated side of the veneer. The spaces within the frames are filled with a mix comprising parts of Leighton Buzzard sand and 3 parts of a solution of a phenol-formaldehyde resin of 75% resin content. In order to facilitate filling, it may be desirable to allow the solvent to evaporate from the mix leaving it dry and free-flowing, but this, in general, produces a somewhat inferior moulded material. If, however, the amount of solvent is comparatively large so that the mix is very wet to the touch, the. strength of the adhesion between the wood and the sand mix will be markedly reduced. A pressure plate is placed in the areas between the retaining walls of the grid and the whole assembly is cured in a heated press.

Example VIII The surfaces of a sheet of soft natural rubber are cyclised by immersion of the rubber in concentrated sul-i phuric acid for five minutes followed by washing in water and drying.

A coating of a suitable thermo-setting phenol or cresol formaldehyde resin adhesive dissolved in alcohol is applied to the surface of the rubber to be placed in-contact with the sand or other suitable inorganic material. The

sand is mixed with 3% of a 70% solution of phenolformaldehyde resin adhesive. The wood veneer or plywood board is coated with a similar resin solution and is placed, resin side up, in the bottom of a flat mould with.

the rubber sheet, resin side up, on top and then the sand mix; and thewhole pressed and cured in one operation at a temperature depending on the heat-resisting properties of the rubber.

It willbe appreciated that the expression water reslstant as used herein and in the appended claims is not used in its strictly technical sense but as denoting an adhesive which will not be attacked or dissolved sufficiently in the presence of moisture as to lose its bonding properties.

Similarly, although the invention has been with reference to composite articles such as floor tiles and panelling .units, it is not intended to exclude articles with such simple curves as the wood veneer or board can conformto.

Example IX 50 parts of Leighton Buzzard sand, 50 parts of Parishs. white silica sand (Erith, Kent), 3 parts of precipitated: chalk and 4 parts of an alcohol solution of a phenol, formaldehyde resin of 70% solids content are thoroughly imixed. A. wood veneer is coated with an epoxy resin solution consisting of l00 parts of a condensation product of epichlorhydrin and p-isopropylidene diphenol having an epoxy content of 2.3 equivalents per kilogram,.60 parts: of methyl cellosolve, 25 parts of china clayand 10 parts 0f triethylenetetramine. The veneer with the adhesive uppermost is ,placed on the bottom of a mould and the sandmix is placed on top and subjected to a momentary pressure of 100 pounds per square inch. A static weight giving apressure of 1 pound per square inch is then placed f on top and the whole heated at a temperature of C.

described for 1 hour. The adhesion of the veneer to the foundation layer is extremely good. The water resistance of the foundation layer is very high and its tensile strength is between 600 and 700 p.s.i.

Example X Example IX was repeated except that instead of the phenol-formaldehyde resin, the same proportion of a mixture of 100 parts of a liquid epoxy resin (prepared from epichlorhydrin and p-isopropylidene diphenol and having an epoxy content of 5.0 equivalents per kilo) and 10 parts of 3-diethylaminopropylamine was employed. The same mixture was used for coating the wood veneer.

No volatile products wereevolved during the cure and a composite article with excellent water-resistance and mechanical strength was obtained.

I claim:

1. A compositearticle having a wood outer face comprising an outer layer of wood veneer at least 0.5 millimeter thick, a backing of sufiicient thickness to resist bending of the article resulting from deformation of the wood caused by swelling and shrinking due to varying moisture content and composed of siliceous granules which are substantially nonabsorbent and of a waterresistant synthetic resin in an amount less than 10% by weight of the material of the backing expressed in terms ofthe combined dry weights of the granules and synthetic resin, faces of said and a bonding layer between the adjacent backing and of said wood veneer consisting of a synthetic resin for adhesively attaching said backing to said wood veneer and constituting between said backing and said wood veneer a barrier substantially impenetrable by moisture. a

2. A composite article having a wood outer face comprising an outer layer of wood veneer at least 0.5 millimeter thick, a backing of sufficient thickness to resist bending of the article resulting from deformation of the wood caused by swelling and shrinking due to varying moisture content and composed of substantially nonab sorbent siliceous granules and ofa water-resistant epoxy resin in an amount less than 10% by weight of the combined dry weights of the granules and epoxy resin, and a bonding layer between the adjacent faces of said backing and of said wood veneer consisting of epoxy resin for adhesively attaching said backing to said wood veneer and constituting a substantially moisture-impenetrable barrier between said backing and said wood veneer.

3. A composite article having a wood outer face comprising an outer layer of wood veneer at least 0.5 millimeter thick, a backing of suflicient thickness to resist bending of the article resulting from deformation of the wood caused by swelling and shrinking due to varying moisture content and composed of substantially nonabsorbent siliceous granules and of a thermo-setting phenolformaldehyde resin in an amount less than 10% by weight of the combined dry weights of the granules and resin, and a bonding layer between the adjacent faces of said backing and of said wood veneer consisting of epoxy resin for adhesively attaching said backing to said wood veneer and constituting a substantially moisture-impenetrable barrier between said backing and said wood veneer.

4. A composite article as set forth in claim 1, wherein the thickness of said backing is at least three times that of said wood veneer.

5. A composite article as set forth in claim 2, wherein the thickness of said backing is at least three times that of said wood veneer.

6. A composite article as set forth in claim 3, wherein the thickness of said backing is at least three times that of said wood veneer.

References Cited inthe file of this patent UNITED STATES PATENTS 

1. A COMPOSITE ARTICLE HAVING WOOD OUTER FACE COMPRISING AN OUTER LAYER OF WOOD VENEER AT LEAST 0.5 MILLIMETER THICK, A BACKING OF SUFFICIENT THICKNESS TO RESIST BENDING OF THE ARTICLE RESULTING FROM DEFORMATION OF THE WOOD CAUSED BY SWELLING AND SHRINKING DUE TO VARYING MOISTURE CONTENT AND COMPOSED OF SILICEOUS GRANULES WHICH ARE SUBSTANTIALLY NONABSORBENT AND OF A WATERRESISTANT SYNTHETIC RESIN IN AN AMOUNT LESS THAN 10% BY WEIGHT OF THE MATERIAL OF THE BACKING EXPRESSED IN TERMS OF THE COMBINED DRY WEIGHTS OF THE GRANULES AND SYNTHETIC RESIN, AND BONDING LAYER BETWEEN THE ADJACENT FACES OF SAID BACKING AND OF SAID WOOD VENEER CONSISTING OF SYNTHETIC RESIN FOR ADHESIVELY ATTACHING SAID BACKING TO SAID WOOD VENEER AND CONSTITUTING BETWEEN SAID BACKING AND SAID WOOD VENEER A BARRIER SUBSTANTIALLY IMPENETRABLE BY MOISTURE. 